Pressure sensitive cover for a fluid port in a downhole tool

ABSTRACT

A fluid port cover for a fluid port includes a disc-shaped body having a weakened material line to render the body tearable.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser. No. 61/709,026 filed on Oct. 2, 2012 and Ser. No. 61/840,847 filed on Jul. 11, 2013, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to downhole tools and, in particular, a fluid port cover for a downhole tool. Apparatus and methods employing the fluid port cover are also described.

BACKGROUND OF THE INVENTION

Port closures, such as a sliding sleeve, a gate, a mandrel, a valve, a detachable cover (i.e. Kobe), a retainer holding the detachable cover in place, etc., are used in wellbore tubular strings and tools to permit selective opening of ports. The ports may provide fluid access between the annulus and the inner diameter of the tubing string or may provide fluid communication to and from a tool on the string, such as a packer.

Some common port closures are opened by pressure driven tools. For example, a common port closure is a hydraulic sleeve that is used in various tools and includes an annular sealing area on the sleeve that is formed to accept and catch thereon a suitably sized plug, such as a ball or other plug form, thereon. When a ball lands thereon, a seal is at least temporarily formed between the ball and the sealing area of the sleeve that inhibits fluid flow therepast such that a hydraulic pressure can be built up above the ball, such hydraulic pressure being suitable to move the sleeve along the tubular in which it is installed. One possible sleeve and ball system is described in U.S. Pat. No. 6,907,936 of Jun. 21, 2005 to the assignee of the present application. That system employs a constriction in the sleeve that forms a seat. Other sleeves may have collapsible seats formed to temporarily catch the plug and hold it long enough to shift the sleeve, before the seat collapses and allows the ball to pass. Other sleeves have non-protruding sealing areas and the plug deforms to squeeze through the sleeve. In these sleeves, the ball when squeezing through the sleeve applies sufficient pressure on the sleeve to shift it. When the ball moves out of the sleeve, it resiliently reforms and can act on another sleeve downhole.

Where the ball is intended to move on to other tools downhole and act again in response to pressure thereon, the string's pressure must be substantially maintained in order to keep the ball moving, even though sleeves may have been actuated to open uphole. Accordingly, it is sometimes desirable that the actual opening of the port to significant fluid flow therethrough be somewhat delayed after the port's closure is actually opened.

SUMMARY OF THE INVENTION

In accordance with a broad aspect of the present invention, there is provided a fluid port cover for a fluid port comprising a disc-shaped body having a weakened material line to render the body tearable, and at least one leak aperture formed through the body, the leak aperture intersecting the weakened material line from which tearing of the body along the weakened material line is initiated when a pressure differential across the body is reached.

In accordance with another broad aspect of the present invention, there is provided a downhole tool assembly comprising: a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; and a fluid port cover comprising a disc-shaped body having a weakened material line to render the body tearable along the weakened material line, and at least one leak aperture formed through the body and intersecting the weakened material line, from which tearing of the body along the material line is initiated when a pressure differential across the body is reached.

In accordance with another broad aspect of the present invention, there is provided a method for operating a downhole tool, the method comprising: providing a downhole tool including a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; a fluid port cover installed in the fluid port; positioning the downhole tool within a wellbore; and creating a pressure differential across the fluid port cover to initiate a tear in the fluid port cover.

It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all within the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIGS. 1A to 1D are sections through a downhole tool. FIG. 1A shows the tool in position downhole before actuation thereof; FIGS. 1B and 1C show a plug acting on the tool to open a port closure and expose a fluid flow to a port cover; and FIG. 1D shows the downhole tool after a period of delay in which the port cover has been removed.

FIG. 2A is a perspective view of a fluid port cover according to an aspect of the present invention. FIG. 2B is a sectional view along line I-I of FIG. 2A.

FIG. 3A is a perspective view of a fluid port cover according to another aspect of the present invention. FIG. 3B is a sectional view along line II-II of FIG. 3A.

FIG. 4 is a sectional view of a fluid port cover installed in a fluid port of a wellbore tool.

FIG. 5A is a sectional view of a fluid port cover installed in a tool and in a first stage of exposure to fluid pressure. FIG. 5B is a perspective view of the fluid port cover installed in a fluid port of a wellbore tool and in an initial alternate stage of opening. FIGS. 5C and 5D are sectional views of the fluid port cover in the same stage as FIG. 5B, and in a later stage, respectively, of opening.

FIGS. 6A and 6B are sectional views of a wellbore string installed in a wellbore and showing two consecutive stages of operation.

DESCRIPTION OF VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

As noted above, port closures are used in wellbore tubular strings and tools to permit selective opening of ports to provide fluid access between the outer diameter and the inner diameter of the tubing string, which may provide access between the annulus about the string and the inner diameter or may provide fluid communication to and from a tool on the string, such as a packer and the inner diameter. Sometimes, although a port closure is actuated to open, it is desirable that the actual opening of the port to fluid flow be somewhat delayed. For example, sometimes it is useful that a tubing string hold pressure long enough to ensure that all pressure driven operations are completed before a port opens to fluid flow therethrough. The port may be actuated to open in response to a pressured up condition, but if it opened at that time, the pressure condition in the tubing string would be disadvantageously lost.

In other instances, a plurality of closures are provided that are each actuable to open one or more ports. Sometimes, where it is desired to open a number of closures in one operation, a pressure driven tool is driven through the string that acts on each of the plurality of closures in turn to open the ports regulated thereby. However, since the closures each open in turn as they are actuated, the pump pressures required to keep the pressure driven tool moving along the string are significant. In particular, each time a closure is actuated to open its port, an amount of fluid can escape through that port. Each port opening therefore dissipates the pressure of the driving fluid in the string, which is intended to act on the pressure driven tool. Limited entry systems may be employed, therefore, to restrict the amount of fluid that can flow through each opened port. It is difficult to use such pressure driven tools to open a plurality of sleeves, if limited entry systems are not also used, and even if the ports are equipped with limited entry inserts, the pump pressure may still be compromised after a number of the ports are opened. As such, it is sometimes desirable that the port opening be delayed after the actual actuation of the port closure to begin moving toward the open position.

Accordingly, in one embodiment, the invention comprises a fluid port cover for a fluid port comprising a disc-shaped body having a weakened material line to render the body progressively splittable along the line, and at least one leak aperture formed through the body.

In one embodiment, the invention comprises a downhole tool assembly comprising a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; and a fluid port cover comprising a disc-shaped body having a weakened material line to render the body progressively separable along the line, and at least one leak aperture formed through the body, through which a flow of fluid can pass to cause erosion of the fluid port cover.

One embodiment of a wellbore tubular port closure system is shown in FIGS. 1A to 1D. The illustrated system includes a downhole tool 2 and a plug for actuating the tool.

Downhole tool 2 may include a fluid port 4, which extends through the wall of the tubular housing. The port extends from the inner diameter ID of the tubular housing to the outer surface 2 a, thereby, when open, providing fluid access through the wall. The port 4 may have a fluid controller to control aspects of the flow therethrough, such as for example, a nozzle, a screen, a choke such as a limited entry insert, etc. A fluid port cover 10 is installed in the fluid port 4. A closure, which in this embodiment is sliding sleeve 8, may be installed to cover the fluid port 4 and may be configurable between a port-closed and a port-open position. The open position exposes the fluid port 4 to fluid flows from the inner diameter.

The sliding sleeve 8 is installed to be axially moveable between the port-closed and the port-open position, particularly between a position overlying the fluid port 4 and a position exposing the fluid port 4 to fluid in the inner diameter and therefore pressure differentials between the inner diameter and the outer surface 2 a of the tool 2. The sleeve 8 may be axially moved, for example, by a plug such as ball 9 passing therethrough. The sleeve 8 moves only when the force applied against the sleeve 8 is sufficient to shear a releasable mechanism such as a shear pin 7. In this embodiment, sufficient force is applied to the move the sleeve when the ball is driven by fluid pressure, arrows P, to squeeze through the sleeve (FIGS. 1B and 1C).

In the open position, as shown in FIG. 1C, the fluid port 4 is exposed so that fluid pressure may be communicated to the fluid port 4. However, although port 4 is exposed, the fluid port cover 10 closes the fluid port 4 so that pressure, except possibly for a small leaking flow (arrows L) through leak apertures 22, may be held in the tool 2. Thus, fluid pressure P in inner diameter ID may be substantially maintained even though sleeve 8 has been moved to expose port 4. Full flow through port 4 is thus not possible and therefore, when the sleeve 8 exposes the fluid port 4, a pressure differential may be developed across the thickness of the fluid port cover 10. However, the fluid port cover 10 may be overcome to open fully (FIG. 1D) after a delay. Once open, fluid can flow, arrows F, through port 4 in a manner only restricted by any flow controller in the port.

The delay may be sufficient to allow the pressure P to be substantially maintained for a selected period of time for example which is suitable to allow tubing operations requiring the pressure P to be concluded. For example, this may be a time suitable to allow ball 8 to pass through the string and actuate one or more further tools, as by shifting sleeves covering further ports or to allow pressure actuation of other tools apart from those actuated by ball 8. This suitable time may, for example, be at least a few seconds, for example at least 5 seconds.

It is desirable that the opening process of fluid port cover 10 progress in a slower manner, for example over the selected period of time noted above, rather than an abrupt, sudden failure, such that there is not a sudden pressure loss in the tubing string that may prevent the full opening of other fluid port covers. The opening process of cover 10 can be by erosion and/or by failure along a line of weakness in the cover material. Failure along the line of weakness can be by the process of tearing wherein the opening progresses more slowly. Because the opening can proceed by one or both of two processes, this offers redundancy to ensure that the opening process can be completed in one or more ways. The opening process is generally intended to at least be initiated by erosion, but can include failure along the line of weakness if the erosion fails, for example the leaking fluid flow is not erosive enough or the erosive flow is stopped.

If the fluid port cover opens by some failure, because the fluid port cover is formed of erodible material, it may continue to erode provided there is a fluid flow through the port, past the fluid port cover.

As noted above, delay of the port opening and gradual opening of fluid port cover 10 may be desirable in particular situations including for example, where a tubing string is to hold pressure long enough to ensure that all pressure driven operations are completed before a port opens to fluid flow therethrough, or where pump pressure is to be maintained to keep a pressure driven tool moving along the string despite multiple closures opening corresponding ports in turn as they are actuated. The pressure driven tool may take various forms, for example, it may be single or multipart. In one embodiment, the pressure driven tool includes a conveyed part, such as a ball 9 that lands against a release mechanism such as a sleeve 8 to be actuated by the ball. For example, where the ball applies a pressure by squeezing through or against a seat. Delayed opening of the fluid port(s) thus minimizes pressure losses, ensuring that pressure conditions in the tool and possibly the tubing string in which the tool is attached are not jeopardized.

A fluid port cover 10 includes a disc-shaped body, which has a thickness t which is relatively small compared to its diameter d. Because of the disc-shaped form, the fluid port cover 10 can be considered to include a first face 12, an opposite face 14 and edges 16 that span the thickness between the first face 12 and the opposite face 14. Generally, the fluid port cover 10 is circular and thus the edges 16 form a circle.

The body faces 12, 14 can be formed in various ways. In one embodiment (FIG. 3B), one or both of the body faces may be planar. This offers the simplest approach to manufacture. In other embodiments (FIG. 4), one or both of the body faces are contoured for various purposes such as fitting with other parts, installation and pressure focusing. For example, the inner facing face, for example in this embodiment, first face 212 may be formed to focus pressure to a particular spot, for example the center. For example, face 212 may have an indent, which gives the face a concave shape and has an inner diameter that tapers toward a centrally oriented point.

Alternately or in addition, as shown in FIG. 2A, the perimeter of one or both faces may be contoured to accept a mounting ring or a sealing ring. For example, in one embodiment, a perimeter 14 a of the opposite face 14 may be recessed relative to a central portion 14 b and may be polished to accept a seal thereagainst. Because the perimeter 14 a, in this embodiment, is retained beneath a seal and/or a retainer, central portion 14 b is that surface of the fluid port cover 10 that is exposed most to pressure differentials.

In one embodiment, the disc-shaped body comprises a circular dome-shaped central portion 14 b and an outer perimeter 14 a, the central portion may be thinner than the perimeter.

The fluid port cover 10 may be formed of a material that is durable in wellbore conditions. The material may be deformable and, if desired, may be erodible when subjected to contact with wellbore fluids or sustained wellbore fluid flows therepast and can fail for example, be separated by tearing, etc. when subjected to over pressurization. The fluid port cover 10 may, for example, be formed of metal, polymers, etc. Suitable materials include, but are not limited to, aluminum and steel such as stainless steel or steel alloys.

As used herein, the terms “eroded”, “erodible” or forms thereof, mean that the fluid port cover 10 or a portion thereof, exhibits substantial mass or density reduction, or chemical transformation when subjected to maintained fluid contact and possibly flows therepast. Mass reduction can occur by for example, dissolution, degradation, wear or fragmentation of the material that forms the fluid port cover 10 by passing fluid or solids. As used herein, the term “solids” means those solids that generally exist in a wellbore, result from operations or is added to achieve selected fluid or operational properties, including from/for drilling, stimulation, perforation, cementing operations, etc. Solids, therefore include naturally occurring debris such as rock particles, sand, silts or clays and introduced particles such as cuttings, mud particulate, proppants, etc.

Chemical transformation can include oxidation/reduction, hydrolysis, substitution, and/or addition reactions, or other chemical reactions of the material from which the fluid port cover 10 is made. The erosion may be the result of a chemical interaction of the fluid port cover 10 with the environment. The erosion may also be triggered by applying a triggering influence, such as a chemical reactant to the fluid port cover 10 for example, to increase a reaction rate. Stimulation fluids such as fracturing fluids, acids, cleaning chemicals, or proppant laden fluids may also cause or facilitate erosion of the fluid port cover 10.

The fluid port cover 10 is formed to gradually separate, split or tear, etc. when exposed to a pressure differential from the first face 12 to the opposite face 14. The failure can be facilitated by a weakened material line 20 on the fluid port cover 10. The material along the line being weaker than the other material of the cover, tends to fail ahead of the other material of the cover. Thus, the gradual failure (splitting, separation, tearing, etc.) of the cover 10 happens along the weakened material line.

The weakened material line may be a plurality of adjacent points or a continuous line. It may be a score, a perforated line, a treated area, a butt connection of two parts, etc. A score may be a scratch, a groove, a cut, an indentation, a trough, etc., and can be formed in many possible ways.

The weakened material line may be straight or curved. There may be one or more such lines. In one embodiment, there may be a plurality of weakened material lines 20 and they may be arrayed in various patterns. Generally, the pattern may be selected to control the way in which cover 10 opens, for example, to control whether portions become detached, fold back, etc. For example, if it is undesirable that pieces of the cover become loose in the well, the weakened material lines can be placed to avoid a continuous enclosed shape (i.e. there are no shapes completely surrounded by a weakened material line).

In one embodiment, as shown in FIG. 2, the weakened material line 20 is a score formed in the material of the fluid port cover 10. To illustrate various options, FIG. 2B shows a flat bottom score and FIGS. 3A and 3B shows a v-shaped score.

Further, in the embodiments shown in FIG. 2A and FIG. 3A, there are two scores on at least the opposite face that form weakened material lines 20, 120. As can be seen, there may be two or more elongate score lines extending from side to side of a portion exposed to a pressure differential, for example central portion 14 b, 140 b and oriented to cross. While the two illustrated score lines are shown crossing each other to form an X and intersecting substantially orthogonally at a center point, other orientations of score lines may be suitable.

In FIG. 2A, the weakened material lines at least extend to some degree across the portion of cover 10 that is open to fluid pressure on both sides and, therefore, across which a pressure differential is generated. In this embodiment that portion is central portion 14 b of the fluid port cover 10. It is desirable to have all portions of the failed fluid port cover 10 remaining attached for example, at the edges 16 to avoid the generation of loose fragments that may interfere with operations. For example, since the score lines have terminating ends (do not form complete circles) and extend from or through a central area on the cover with ends extending toward an edge of the fluid port cover 10, there is no portion of the fluid port cover 10 from which a loose fragment can be generated. Thus, while various score patterns may be used, score lines that intersect as shown forming an X shape may be useful since, when the fluid port cover 10 begins to open, the central portion 14 b tears along the score lines in segments similar to triangular flaps which extend outwardly and fold back in the direction of the out flowing fluid. Opening in this way reduces the risk of cover 10 detachment or fragmentation, and minimizes restriction of fluid flow through the fluid port cover 10. The embodiment shown in FIG. 2A has two intersecting weakened material lines 20 formed as scores that form four segments which will extend in the direction of the fluid flow. However, other embodiments may have three or more score lines to produce a correspondingly greater number of folded back segments upon opening.

The opening of the fluid port cover 10 occurs when a suitable pressure differential is achieved from side 12 to side 14. The pressure differential at which failure occurs is dependent upon several factors including, but not limited to, the type and thickness of the material of which the fluid port cover 10 is made; and the number, spacing and pattern (density) and form (i.e. length, shape, depth) of the lines 20 of material weakness. Of course, as soon as a closure, such as sleeve 8, over the port is opened, a pressure will be communicated to the cover 10. If an elevated pressure is required for tubing operations, a pressure differential is likely to be generated across the exposed cover, wherein tubing pressure is greater than the pressure external to the tool. However, in such a situation, it is likely that the cover is not intended to fail at that pressure differential since such failure would jeopardize the tubing operations. Thus, the suitable pressure differential for cover failure may be higher than the pressure differential required for tubing operations to be carried out before full opening of the ports and the resultant tubing pressure loss.

As noted, it is useful if the weakened material line opens gradually, as opposed to all at once. In one embodiment, therefore, the weakened material line may be formed to tear. As used herein, the terms “tear”, “tearing” or other related terms means that the fluid port cover 10 separates progressively along the lines 20 when the pressure differential across the fluid port cover 10 is reached: The full length of all the lines on a cover do not open simultaneously. Tearing is considered distinct from “bursting” wherein full opening is achieved rapidly in milliseconds or less using frangible burst or rupture discs as are well known in the art. In contrast, the process of tearing permits slower, gradual opening of the fluid port cover 10 to delay full opening of the fluid port 4 and to provide some resistance to fluid flow even while the process of opening progresses. In one embodiment, progressive opening is provided because the body has a material strength at the weakened material line that varies from one portion of the body at the weakened material line to another portion of the body at the weakened material line. This permits a progressive opening of the body along the weakened material line from the portion of the body that is weaker to the portion of the body that is stronger, when a pressure differential across the body is reached. This progressive opening, termed herein “tearing”, may be achieved by intersection of lines 20 and/or by varying the form (shape, depth, etc.) of the line along its length and/or by varying the thickness of the body over which the lines 20 extend.

For example, in an embodiment employing a score, the thickness of the cover at the score is substantially less than the thickness of other areas of the cover material lacking scores, this renders the material of the body weaker along the lines than elsewhere.

To achieve a progressive opening process, the shape of the score may be selected. For example, the V-shaped depth of a score, as shown in FIGS. 3A and 3B, focuses the stresses to the thinnest point in the score. The more sharp the V-shape, the more frangible the score. Thus, the V-shape can be varied along the length from a cross sectional shape with a sharply V-shaped bottom, which will fail first, to a more rounded or flattened bottom shape, into which a tear will propagate after the initial failing.

Alternately or in addition, to achieve a progressive opening process, the scores may be deeper along one length than another such that one length is weaker than the other. For example, the central area of the scores (which are identified as lines 20 in FIG. 2A) near their intersection may be deeper than other areas of the scores, so that the cover's body material at the lines in the central area is thinner and thereby weaker than the cover's body material at the outer end of the lines. Thus, the cover at lines 20 near their intersection is able to split first, while the remaining length of the lines 20 will separate later in time, the effect being that the line 20 opens progressively, i.e. tears, along its length from the intersection outwardly. Alternately, as shown in FIG. 4, the thickness of the cover 210 may vary across the face 214 b where the score 220 extends. In this embodiment backside 212 of the cover 210 is formed concavely, with an inner diameter tapering toward a centrally located point, such that one area 210′ of the cover at score 220 is thinner and thereby weaker, than another area 210″ of the cover. Area 210′ is weaker and will therefore fail first resulting in a progressive opening (i.e. tearing) of the cover along score 220 from area 210′ to area 210″.

In one embodiment, such as is shown in FIGS. 3A and 3B, at least one small “leak” aperture 122 may be formed in a location on the fluid port cover 110. The leak aperture 122 is a small diameter, normally open, aperture passing through the cover extending from side 112 to side 114 to provide for a small degree of fluid communication therethrough across the cover.

Fluid port cover 110 may be as described above except with respect to aperture 122 and the shape of weakened material lines 120. Fluid port cover 110 may also include one or more weakened material lines 120, but which are V-shaped as noted above.

The leak aperture may act as a point at which a fluid flow can pass through the cover, even at pressures less than the failure differential described above. Thus, leak aperture 122 provides a point at which erosion can occur and/or where a tear along lines 120 can be initiated. An advantageous position for the leak aperture may be adjacent or through a weakened material line. For example, weakened material line 120 may extend from or through the leak aperture 122. In one embodiment, an advantageous position for the leak aperture 122 is in the central portion 140 b of the fluid port cover 110 where two or more weakened material lines 120 intersect.

The leak aperture 122 should preferably be sized to permit a flow of fluid therethrough but without significantly releasing pressure from the inner diameter. The flow of fluid through the leak aperture 122 may have an erosive effect which slowly and gradually opens the port to full flow therethrough. Generally, the leak aperture may prevent the suitable failure pressure for the cover from being reached. Thus, erosion may be the primary process by which the cover opens. However, if the leak aperture becomes plugged, or excessive ID pressures are encountered, cover may fail at lines 120. Thus, there is redundancy. Further, if the leak aperture is adjacent or intersects a material line 120, leak aperture 122 may also facilitate the initial tearing of the fluid port cover 110 to permit a gradual tear to open the fluid port in which cover 110 is installed.

While a range of different diameters can be used for the leak aperture 122, a diameter of between about 0.5 mm to about 5 mm may be effective in achieving the leak aperture's purposes. While typically circular, the leak aperture 122 can be of other shapes such as, for example, ovals, square, rectangular, hexagonal, star shaped, etc.

Various mechanisms may be used for installing the fluid port cover 10, 110 in the fluid port 4; for example, the fluid port cover 10 may be press fit or machined within the fluid port 4. Alternately, as shown in FIG. 3B, the fluid port cover 110 may be installed in a body 102 to be installed in the wall of the tool. The body may be configured with threads 160 for mating with corresponding threads within a hole in the tool body wall. In such an embodiment, the fluid port in which cover 110 is installed is a bore 104 through body 102. In one embodiment, the body may carry a jet nozzle 130 that has an opening formed to affect fluid flows therethrough including metering the flow such as modifying the force, fluid velocity, rate and pressure of the fluid passing through the bore. The shape, and therefor the fluid effect of the jet nozzle, may be selectable for the fluid effects of interest. As such, jet nozzle 130 may be a separate part than the body and may be installed for example by a retainer ring. In this illustrated embodiment, fluid port cover 110 is positioned outwardly of nozzle 130 such that after fluid passes through the nozzle opening it contacts the port cover 110.

FIG. 4 shows a fluid port cover 210 similar to that of FIG. 3B with a score 220 and a leak aperture 222. Cover 210 is installed in a fluid port 204 of a tool 202 with a retainer 224 installed and a seal 236 over the perimeter edges 214 a of the fluid port cover 210, leaving the central portion 214 b exposed. The retainer 224 includes a ring that fits into a gland 225 in the wall of the port 204. Seal 236 is an O-ring pressed between a flow controller in the form of an annular insert 230 and the perimeter 214 a of the fluid port cover 210.

In one embodiment, the insert 230 is formed as a nozzle to generate a jetting effect on fluid flows passing therethrough. The nozzle insert 230 may include a convergent type orifice, having a fluid opening that narrows from a wide diameter to a smaller diameter in the direction of the fluid flow, thereby acting in a limited entry system to restrict the amount of fluid which can flow through the fluid port 4 after it is fully open. This controls the characteristics of the fluid passing through the port and, where there are many such ports opened in the string, ensures that pressure can be maintained and consistently distributed in the string. Different sizes of nozzle insert 230 may be used. The “size” of the nozzle insert 230 relates to the size of the fluid port 4 and the orifice diameter, which dictates the characteristics of the fluid in terms of velocity and pressure drop to be effected by passage through the nozzle insert. The nozzle insert 230 may be formed of substantially non-erodible material such as carbide, harder steel alloys and stainless steel, or other suitable material.

When fluid port cover 210 is intact, the nozzle insert 230 supports perimeter 214 a and may focus fluid pressure from the inner diameter ID of the tool onto the fluid port cover 210 at area 214 b which spans the orifice of the nozzle insert, thus facilitating erosion through leak aperture 222 or failure along scores 220.

FIGS. 5A-5D show an opening process of a fluid port cover 310. The opening begins after the port 304 and therefore fluid port cover 310 in port 304, is exposed to a pressure from the inner diameter ID of the tool 302 in which it is installed. This may occur by the removal of a closure such as sleeve 8 from over the port (FIG. 1C). When the inner diameter ID is pressured up and this fluid pressure is exposed to cover 310, a leaking amount, arrow L, of fluid can pass through leak aperture 322 (FIG. 5A). While this amount is insufficient to eliminate the generation of a pressure differential across (i.e. between inner side 312 and outside 314) cover 310, it may be sufficient to remove the cover gradually by erosion about aperture 322.

If erosive effects do not open cover 310, for example, if aperture 322 becomes clogged by debris D (FIGS. 5B and 5C), the cover can be made to fail by increasing the pressure differential across cover 310. In particular, when a suitable pressure differential is developed across the fluid port cover 310, tears T begin to form along the weakened material lines 320. Because the portion of lines 320 adjacent aperture 322 may be weaker as by damage, reduced thickness or sharper V-shaped depth, and therefore weaker, area of cover 310, the tear T may begin at the lines adjacent aperture 322 and progress outwardly. If the pressure differential is maintained, the tear continues to generate a larger opening through the fluid port cover 310. The tears allow the separated parts to fold back away from the high pressure ID and along the direction of fluid flow, arrows F. Erosion E by fluid flowing, arrows F, past the erodible material of the cover may enlarge the opening through cover and wear away the segments that fold back out of the way, along the direction of flow (FIG. 5D). Over time, erosion may remove the fluid port cover 310 entirely to fully expose the orifice of nozzle insert 330 to the fluid flows therethrough.

The pressure to initiate the tear may be selected based on the pressure profiles of the process. In one embodiment, the pressure is selected to be greater than the pressure required to move the closure opening tool (ball 9) or to reconfigure, for example open, the closure (sleeve 8). For example, the pressure selected for initiating a tear may be greater than the pressure required to shift a sleeve and greater than that pressure necessary to keep the ball moving through the string. While the pressure for initiating a tear may have any upper limit, consideration may be given to pump pressures attainable and failure parameters of the tools. Generally, the pressure to initiate a tear may be quite reasonable but above the pressure to reconfigure the closures. For example, in one embodiment, the pressure to initiate a tear is selected to be about 1.5 to 2 times the pressure required to reconfigure a closure.

In one embodiment, the invention comprises a method for operating a downhole tool. The method includes providing a downhole tool with a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; a fluid port cover installed in the fluid port; positioning the downhole tool within a wellbore; creating a pressure differential across the fluid port cover to cause an erosive flow through the port; and increasing the pressure to initiate a tear in the fluid port cover.

The tool may be the only tool intended for operation in the well or, as shown in FIGS. 6A and 6B, there may be a plurality of tools 402 a, 402 b connected in a string. The tools may be actuated, in turn but in one trip past, by a single fluid conveyed tool, such as ball 409.

The tools for example may each have a tubular wall through which extends a fluid port 404 that, when fully open, permits fluid flow from the inner diameter ID of the string to the annulus A about the tool.

Each tool further includes a closure 408 a, 408 b isolating their fluid port from pressures in the inner diameter, until the closures are removed from a covering position over the fluid port. Closures 408 a, 408 b are normally held in a port closing position by a releasable lock 417. The lock may be overcome to permit reconfiguration, in this embodiment movement against a stop 460 and therefore port opening, of the closures when acted upon by tool 409. In this embodiment, closure 408 a includes a collapsible ball seat 411 a on which ball lands and at least temporarily seals to create a piston effect to move the closure. Thereafter, ball causes seat 411 a to collapse and ball 409 continues to closure 408 b. This closure has a non-collapsible ball seat 411 b on which ball 409 lands and seals so that closure 408 b is moved by pressure acting against the ball and the seat. Unlike seat 411 a, however, seat 411 b retains ball such that the string uphole of ball 409, and in which ports 404 are exposed, can be pressured up.

As will be appreciated by the teachings hereinbefore, the pressure in the string cannot be lost when closure 408 a is moved to the port open position because pressure is required to move ball 409 through seat 411 a, into tool 402 b and against seat 411 b with enough force to move closure 408 b. Thus, a fluid port cover 410 is installed in at least the port of tool 402 a, but herein also in the port of tool 402 b. Fluid port covers 410 each have the features described hereinbefore of the weakened material lines, leak aperture and erodibility to ensure that each fluid port cover may operate reliably in a controlled manner to delay opening of its fluid port 404, after that fluid port is exposed to tubing pressure. First, each fluid port cover will begin to experience a leading flow through its leak aperture, which may cause erosion and therefore gradual opening of the port. Occasions may arise where the leak aperture of one or more covers 410 may be blocked by debris or the cover may otherwise fail to erode, thereby impeding the removal of the fluid port cover. Regardless of such failures, each cover 410 offers opening redundancy and, when a suitable pressure differential is reached can fail, and may fail, as by tearing, along weakened material lines so that the fluid port cover 410 opens in a gradual way. This ensures that pressure is not lost rapidly in the tubing string and fluid pressures and differentials remain so that other ports can be acted upon to open by erosion and/or failure as well. Further, the fluid port cover 410 is formed of material which is erodible, for example, by fluid or debris, such that the fluid port cover 410 may be eventually entirely removed from over the fluid port 404 and to expose the fluid port and any flow controller therein, such as a nozzle insert, to maximum fluid flow therethrough.

Once the fluid ports 404 are opened, the wellbore processes intended to be effected through the string can proceed. For example, in one embodiment wellbore treatment fluids are injected out from the tubing string through the fluid ports 404 to the wellbore to fluid treat, for example, to fracture the formation accessed by the wellbore W. Although the fluid flow cover 410 has particular utility for a fracturing operation, it can be used for other applications including for example, petroleum refining and petrochemical operations, testing the integrity of connections between sections of tubing strings, or other uses in which a fluid is conveyed under pressure through a conduit and delayed opening of fluid port(s) is desirable to maintain optimal pressure conditions and/or to reduce pressure losses.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”. 

1. A fluid port cover for a fluid port comprising: a fluid port cover for a fluid port comprising a disc-shaped body having a weakened material line to render the body tearable, and at least one leak aperture formed through the body, the leak aperture intersecting the weakened material line from which tearing of the body along the weakened material line is initiated when a pressure differential across the body is reached.
 2. The cover of claim 1, wherein the body is formed of an erodible material.
 3. The cover of claim 1, wherein the body has a material strength at the weakened material line that varies from one portion of the weakened material line to a second portion of the weakened material line to permit a progressive opening of the body along the weakened material line when a pressure differential across the body is reached.
 4. The cover of claim 3, wherein the body comprises a first face, an opposite face, and edges between the first face and the opposite face and the body has a thickness from the first face to the opposite face varies and the thickness varies from the one portion of the weakened material line to the second portion of the weakened material line to cause the variance in the material strength of the body.
 5. The cover of claim 4 wherein the first face is substantially planar and the opposite face is concave with a tapering inner diameter that tapers toward a substantially central point between the edges and the weakened material line extends along a length of the first face opposite the tapering inner diameter.
 6. The cover of claim 1, wherein the weakened material line is a score and the score has a depth that varies along its length to cause the variance in the material strength of the body.
 7. The cover of claim 6, wherein the perimeter of the opposite face is recessed relative to the central portion to receive the mounting ring or the sealing ring.
 8. The cover of claim 1, wherein the weakened material line includes a plurality of score lines crossing at an intersecting point on at least one side face of the body, the body adjacent the intersecting point having a strength weaker than a portion of the body distanced from the intersecting point.
 9. The cover of claim 1, wherein the weakened material line is a V-shaped score.
 10. The cover of claim 9, wherein the body is formed of aluminum or steel.
 11. A downhole tool assembly comprising: a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; and the fluid port cover of claim 1 installed in the fluid port.
 12. The assembly of claim 11, wherein the fluid port cover is sealed against the fluid port by a seal compressed in the fluid port between an annular insert and the perimeter of the fluid port cover.
 13. The assembly of claim 12, wherein the annular insert is selected to meter fluid flow through the port.
 14. The assembly of claim 12, wherein the annular insert comprises a nozzle defining a flow path for fluid therethrough.
 15. The assembly of claim 12, wherein the fluid port comprises a gland in its wall for receiving a retaining ring for securing the insert against the seal and the fluid port cover.
 16. The assembly of claim 11, wherein the closure comprises a sliding sleeve.
 17. A method for operating a downhole tool comprising: providing a downhole tool including a tubular body including a wall forming an inner diameter and an outer surface; a fluid port through the tubular body; a closure installed to be configurable between a position covering the fluid port and a position exposing the fluid port; and the fluid port cover of claim 1 installed in the fluid port; positioning the downhole tool within a wellbore; and creating a pressure differential across the fluid port cover to initiate a tear in the fluid port cover.
 18. The method of claim 17, wherein the closure comprises a sliding sleeve.
 19. The method of claim 17, further comprising metering fluid flow through the fluid port. 